1. Field of Invention
The present invention relates to power conversion, and more particularly, to synchronizing frequency and phase of multiple variable frequency power converters.
2. Description of Related Art
Power converters are essential for many modern electronic devices. Among other capabilities, a power converter can adjust voltage level downward (buck converter and its derivatives) or adjust voltage level upward (boost converter and its derivatives). A power converter may also convert from alternating current (AC) power to direct current (DC) power, or vice versa. A power converter may also function to provide an output at a regulated level (e.g., 5.0V). Power converters are typically implemented using one or more switching devices, such as transistors, which are turned on and off to deliver power to the output of the converter. Control circuitry is provided to regulate the turning on and off of the switching devices, and thus, these converters are known as “switching regulators” or “switching converters.” Such a power converter may be incorporated into or used to implement a power supply—i.e., a switching mode power supply (SMPS). The power converters may also include one or more capacitors or inductors for alternately storing and outputting energy.
In some switching power converters, the frequency at which the switching devices are turned on and off may vary. Such power converters are known as variable frequency power converters and can include, for example, boundary conduction mode (BCM) power factor correction (PFC), quasi-resonant flyback converters, resonant converters, etc. Variable frequency power converters operate at their natural frequencies, which can depend on or be defined by their component values and operating conditions. Because most components are made to tolerances (i.e., a range of variation), the natural frequencies of variable frequency power converters (even of the same design) can be different, thus making it difficult to synchronize them.
Variable frequency power converters can have three time domain functions—synchronization, maximum frequency limit, and minimum frequency limit. The three time domain functions are usually implemented by independent time bases—i.e., each has its own timer or oscillator with its respective tolerances—making synchronization even more difficult when the converter is not in normal operation (i.e., in either frequency limit). In analog implementations, one problem is that the maximum frequency limit requires a short timer; the minimum frequency limit requires a long timer; and synchronization must work over a wide frequency range since synchronized operation is required at all times. The matching of these various timers, if implemented in analog circuitry, is very difficult.